1. Field of the Invention
The present invention relates to an organic electroluminescent display panel or device comprising in matrix a plurality of organic electroluminescent elements (also referred to herein as EL elements) each including an emitting layer made of an organic compound material, which utilizes an electroluminescence phenomenon that is the emission of light resulting from injection of an electric current to the emitting layer.
2. Description of the Related Art
Generally, an organic EL element comprises one or more organic function layers made of EL media disposed between a cathode and an anode. In micro-patterning steps for forming the cathode and the organic function layers, there is a difficulty due to low levels in durabilities of heat resistance (e.g., 100 centigrade degree or less), wet-proof and solvent-resisting characteristic. In case that the ordinary photolithography patterning is utilized for the formation of such function layers of the organic EL element, the solvent in the photoresist may infiltrate into the function layers of the EL element. Such an organic EL element suffers from a high temperature atmosphere during pre-baking of the photoresist. The development solution or etching liquid for the photoresist layer may also intrude into the organic EL element. These procedures probably damage the EL element. Even plasma in the dry-etching for the photoresist layer damages the organic function layers of the EL element. These damages cause the deterioration in performance of the organic EL element and the emission property thereof. This is a serious problem.
Alternatively, there is a vacuum deposit patterning process for forming the cathode in the organic EL element by using a shadow mask to be put on the substrate on which the anode and the organic function layers are previously formed. In this case, there are also many problems. That is, the leakage of the vapor of cathode material occurs between the mask and the substrate due to an incomplete contact thereof. Otherwise, the shadow mask is compulsorily, sealingly put into contact with the substrate or the organic function layers. In this case, the organic function layer is physically damaged due to the contact of the forced mask during the deposition, so that resultant cathode comes into contact with the anode to be short-circuited. In addition, the mask is apt to be warped because of insufficient strength of the mask having a great number of openings for such stripe patterns in an large area as stripe cathode patterns. It is therefore very difficult to form precise fine patterns for the cathode of the organic EL element. There have been known EL display devices as shown in Japanese Patent Kokai Nos. 2-66873, 5-275172, 5-258859 and 5-258860, the latter of three corresponding to U.S. patent applications Ser. Nos. 814512, 814163 and 814553 respectively. The disclosed full color EL display device comprises a plurality of emitting pixels existing at intersections of columns and rows of matrix electrodes.
The pixels in the EL device are formed on a common transparent substrate with electrical insulation. The line electrodes made of transparent material are formed on the substrate and spaced from one another. This first transparent electrodes connect the adjacent pixels. Organic EL media are formed on the first electrodes and the substrate. The pixels include the second electrodes of row formed on the organic EL media respectively and spaced from one another. The second electrodes of row extends perpendicular to the first electrodes and connect the adjacent pixels respectively. In the emitting device, there is employed a simple matrix structure that the first and second electrodes sandwich the organic EL media at the intersections thereof.
In the patterning technology disclosed in Japanese Patent Kokai Nos. 5-275172, 5-258859 and 5-258860, such an emitting device is manufactured as follows: Straight higher walls with a height of several or tens micrometers as standing masks are previously formed on the substrate. Then the second electrodes and the organic EL medium thin films are vacuum-deposited in such a manner that such higher wall masks selectively and selectively shield a boundary from a vapor flow of the predetermined organic EL medium which is provided onto the surface of the substrate in only one slanting direction to the substrate.
Such a patterning process has still a difficulty to form such standing wall masks having a high aspect ratio (height/bottom) in its cross-section on the substrate when fine pixels and patterns are fabricated for the full-color display panel. Even if such higher wall masks are formed on the substrate for a fine pattern, the strength of walls will be low and thus the reliability in the performances and shapes of the resultant second electrodes and organic EL media films will be low. For example, there is a probability of collapse of such wall masks during a wire-bonding of a conductive material from outside, so that the organic function layers and the first and the second electrodes are short-circuited.